HR: 0830h
AN: P21A-02    [Abstracts]
TI: Numerical Modeling of the Chicxulub Impact Structure
AU: Collins, G S
EM: g.collins@imperial.ac.uk
AF: Dept. Earth Science and Eng., Imperial College London South Kensington Campus, London, SW7 2AZ United Kingdom
AU: Ivanov, B A
EM: baivanov@idg.chph.ras.ru
AF: Institute for Dynamics of Geospheres, Russian Academy of Sciences Leninsky Prospect, 38-1, Moscow, 119334 Russian Federation
AU: Melosh, H J
EM: jmelosh@lpl.arizona.edu
AF: Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ 85721
AU: * Morgan, J V
EM: j.v.morgan@imperial.ac.uk
AF: Dept. Earth Science and Eng., Imperial College London South Kensington Campus, London, SW7 2AZ United Kingdom
AU: Wuennemann, K
EM: wunnema@lpl.arizona.edu
AF: Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ 85721
AB: The Chicxulub impact structure, Gulf of Mexico, is a large multi-ringed impact crater. It is thought to be near-pristine and, although it is buried under approximately 1.5 km of tertiary sediments, geophysical exploration has provided a wealth of data that have furthered our understanding of large impact crater formation. The buried crater exhibits several structural elements unique to large impact structures, as observed on Earth and other planets: a topographic peak ring; a broad and very shallow profile; a slumped main crater rim; concentric, inward-facing fault-scarps exterior to the main rim; and a central core of higher density than its surroundings, presumably as a result of the uplift of dense, lower-crustal rocks in the crater centre. Despite intense deformation in the crust beneath the crater, the crust-mantle boundary appears to be only modestly distorted beneath the centre of the crater. Numerical simulations of vertical hypervelocity impacts provide a means for testing the physical realism of dynamical models for the formation of large impact structures that have been inspired by interpretations of the geophysical data at Chicxulub. We have developed a suite of closely related Lagrangian and Eulerian numerical codes that offer a realistic description of both the shock wave and high temperature thermodynamics of the impact event and the later, lower temperature processes of rock fracture and structural collapse. In this paper we present some recent simulations of the Chicxulub impact and compare our results with interpretations of the geophysical data. We show that the majority of the structural elements of the crater are all well-reproduced by our collapse simulations: the broad, shallow final-crater profile, the peak ring, the central uplift and the upper-mantle deformation. In particular, our simulations predict that the peak ring at Chicxulub is formed by the interaction of two flow regimes: the inwardly collapsing transient crater rim and the outwardly collapsing central uplift. Although the material that forms the peak ring derives from deeply-buried crustal rock, it is highly strained and likely to be heavily brecciated. Furthermore, our model predicts a final position for the crust-mantle boundary similar to that observed in the seismic data, and an approximately 5-km thick, 90-km wide, melt sheet.
DE: 5400 PLANETOLOGY: SOLID SURFACE PLANETS
DE: 5420 Impact phenomena (includes cratering)
DE: 8010 Fractures and faults
DE: 8020 Mechanics
SC: Planetary Sciences [P]
MN: 2005 Joint Assembly